Scrivener 3.0 Beta vs Scrivener 1.9.16

Should I move to the Beta or stick with the supported version? I am dealing with issues in aspell and would like to try the improved spellcheck, but I don’t know if I should move to the Scrivener 3.0 until it is supported.

If I go to 3.0, this break compatibility with my Mac as it is too old to run Scrivener 3.0 for Mac. I never use the Mac, but I thought I might need it for ebook kerning when I am done with the novel.

So should I stay or should I go now?

The spellcheck is not different 3.0.

… although it may be a newer version.

The best advice, seeing as you didn’t state what issues you are hoping were fixed or worked around, is to install the beta in a folder separate from the default one (so as not to replace the current version). Then convert a project where you’ve been experiencing the issue (Scrivener 3 will create a version 1-compatible backup copy in the same folder before the conversion), and test it out. Don’t do any real work on your project in version 3 until you’re satisfied that it solves whatever issues you’re having (or if it’s the same, but other features tempt you), so that you can just go back to the v1 backup copy using Scrivener 1.

Indeed Scrivener v3 uses Hunspell. Scrivener v1.9 uses Aspell.
Huspell is more popular nowadays and has a lot of dictionaries available for download from multiple locations. Scrivener comes bundled with an average size dictionaries, but you can always replace them with more sophisticated ones from the web.